$(A)$ $A$ pleiotropic gene exhibits multiple phenotypic effects.
$(B)$ Multiple alleles express similar phenotypic expressions.
$(C)$ Polygenes exhibit continuous variation.

• A
  Statements $(A)$,$(B)$,and $(C)$ are correct.
• B
  Statements $(A)$ and $(C)$ are correct,and $(B)$ is incorrect.
• C
  Statements $(A)$,$(B)$,and $(C)$ are incorrect.
• D
  Statements $(B)$ and $(C)$ are correct,and $(A)$ is incorrect.